Junction Loss Experiments: Laboratory Report

Publication No. FHWA-HRT-07-036

December 2006

FOREWORD

The junction loss study described in this report was conducted at the Federal Highway Administration (FHWA) hydraulics laboratory. Between 1986 and 1992, Chang et al. conducted a lab study of energy losses through junction access holes, using relatively large-scale (one-quarter scale) physical models.(1) A preliminary method for determining such losses, based on early results from that study, was published in the Federal Highway Administration's (FHWA) Urban Drainage Design Manual (Hydraulic Engineering Circular No. 22 (HEC 22)).(2)FHWA plans to update HEC 22 and further develop computer software for storm drain design. The need for consistent technology in FHWA publications and software applications on this subject is urgent. To accommodate that need and overcome some of the difficulties in estimating energy loss in access holes, the FHWA's Office of Bridge Technology initiated this study to validate Roger Kilgore's proposed method for computing access hole energy losses. This report will be of interest to hydraulic engineers involved in storm drain design and to researchers involved in developing improved storm drain design guidelines. It is being published as a Web document only.

Gary L. HendersonDirector, Office of InfrastructureResearch and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

The current study has two objectives. The first is to evaluate Roger Kilgore's proposed procedure, which requires conducting some of the same types of tests that were run in the previous study. The new tests conducted include a wider range of parameters, such as greater plunge-height ratios and steeper pipe slopes. Previous research was limited in that it was applicable to storm drain systems located only in relatively flat areas; the research would not hold up for systems in hilly and mountainous regions of the country where steep pipe slopes are the norm.

The second and more challenging objective is to characterize the energy level in an access hole. If that can be accomplished, then the familiar culvert hydraulics analyses can be applied to the access hole that serves as the tailbox where inflow pipes enter and to the headbox for outflow pipes where the water exits. Researchers have attempted numerous analyses of particle image velocimetry (PIV) data and three-dimensional (3–D) numerical model data, with uneven results. Characterizing energy in the access hole is highly problematic because the flow is so chaotic, and arbitrary assumptions had to be made to obtain results that fall between intuitive limits. Researchers at the FHWA lab now have investigated the more organized flow in the contracted area of the outflow pipe, using the contraction ratio as an indirect measure of the contraction loss in the flow from the access hole to the outflow pipe to backcalculate the energy loss in the access hole.